In drilling boreholes, stabilizers are often placed at a location to add stiffness to the drill string so that the string will not bend or move to the sidewall of the hole in response to an opposing force offered by the formation being penetrated. Alternatively, the drill string is sometimes made very limber in order to take advantage of the centrifugal forces associated with the bit rotation. In any event, when a borehole commences to deviate from the vertical, the weight on the bit as well as the rotary speed can be adjusted to oppose and overcome this deviating force. However, the hole often is deviated several degrees before these remedial actions can be employed. Furthermore, these drilling techniques require that the bit weight, rotary speed, and pump pressure be adjusted to a value which increases the cost of making the borehole.
Three coned rock bits are known to those skilled in the art. It is also known in the art to arrange the cutters of a rotary bit whereby a plane passing through the cutters are arranged obliquely respective to the longitudinal axial centerline of the drill string as evidenced by the patents to Seifert U.S. Pat. No. 1,856,437; Catland U.S. Pat. No. 2,154,032; Zublin U.S. Pat. No. 2,336,335; Rossman U.S. Pat. No. 2,362,860; Willis U.S. Pat. No. 4,168,755; Zublin U.S. Pat. No. 2,336,337; and Beeman U.S. Pat. No. 4,372,403.
The present invention differs from the above cited prior art in that the cutterhead, while having only a simple rotational motion about the longitudinal axial centerline thereof and is motionless, is formed with respect to the pin and shank portion of the bit, such that the centerline containing the centroid of any area of the cutterhead arrived at by a vertical cross-sectioning of the bit, will be the obliqued centerline and not the longitudinal axial centerline. Furthermore, the cones, while being arranged obliquely, are located about the cutterhead such that the centroid of the plurality of cutters is located on the oblique centerline and not the longitudinal axial centerline. Also, the placement of the teeth on the cone, whether inserts or milled teeth, is such that if a circle with its center located on the rotational axis of the cone were inscribed on the outer surface of the cone at any specified distance from the plane of the base of the cone, will be such that the described circle intersects a plurality of the teeth.